I installed S-VCM a few weeks ago on my recently purchased 2011, 92,000 miles. I did just this. I spliced on additional wire onto the S-VCM module and ran the wire through the firewall on the driver's side. I wired in a simple 12V toggle switch and double side taped it under the dash hidden and out of size. I then completed the circuit by using a fused "add a circuit" fuse harness and plugged this into the the accessory circuit on the interior fuse panel (which only has power when the key is at the "accessory" position or at the '"on" position). This allows for the S-VCM module to only power on with the ignition.
With the installed toggle switch under the dash, I now can actually turn the VCM system on and off using the toggle switch while driving. Even when powering the S-VCM module on an off while driving does not trigger any check engine lights and runs of VCM 100% of the time with the flip of a switch.
Sorry to pull up this old thread but I was interested to hear more about the switched s-vcm.
I was actually thinking about using the factory ECO switch to engage/disengage the s-vcm. This would give the ECO switch real meaning.
I didn't know if cutting the power to the s-vcm during regular operation would throw a CEL or not.